Blood Clots

Oct 24, 2009

Blood Clots in Lungs Might Not Always Originate in Deep Veins of Legs and Pelvis in Trauma Patients

Few trauma patients who develop potentially deadly blood clots in the lungs (pulmonary embolism) also have clots in the deep veins of their pelvis and legs (deep venous thrombosis), challenging commonly held beliefs about the association between the two conditions, according to a report in the October issue of Archives of Surgery, one of the JAMA/Archives journals.

“For decades, it has been taught that pulmonary embolism is a sequel of deep venous thrombosis,” the authors write as background information in the article. “Forming in the lower extremity or pelvic veins, clots break off and travel to the pulmonary circulation. Therefore, deep venous thrombosis and pulmonary embolism should coexist in most patients, because part of the clot embolizes [lodges] in the lung, and part remains attached to the vein.”

George C. Velmahos, M.D., Ph.D., and colleagues at Massachusetts General Hospital and Harvard Medical School, Boston, studied 247 trauma patients who underwent imaging scans of the lungs and the veins in the pelvis and legs between 2004 and 2006. Demographic information, as well as data on injury type and severity, imaging findings, hospital length of stay and death rates, was collected.

Among the 247 patients, 46 (19 percent) were diagnosed with pulmonary embolism and 18 (7 percent) had deep venous thrombosis. Seven patients with pulmonary embolism (15 percent) also had deep venous thrombosis. There were no differences between patients with pulmonary embolism who did and did not have deep venous thrombosis in any of the demographic or clinical variables assessed.

“Based on these data, there is little evidence that pulmonary embolism originates from deep venous thrombosis of peripheral veins,” the authors conclude. Among the potential explanations for the lack of association are that clots formed in the legs and pelvis completely dislodge when they travel to the lungs; therefore, no evidence of deep venous thrombosis would remain in patients with pulmonary embolism. However, studies on cadavers have shown that typically only part of the clot breaks off and lodges elsewhere.

“We propose that many pulmonary embolisms form primarily in the lungs and that the risk-benefit ratio of vena cava filters [devices designed to trap clots and stop them from traveling to the lungs] should be reconsidered,” they write. “As computed tomographic venography [vein imaging] becomes more popular and accurate, this issue will be further explored, and it may be revealed that (not surprisingly) we have been preaching and practicing the wrong dogma for years.”

Arch Surg. 2009;144[10]:928-932.

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